1. Field of the Invention
The present invention relates in general to the field of liquid crystal display (LCD) systems. More particularly, the present invention relates to a liquid crystal display that is illuminated with collimated backlighting. In a preferred embodiment, the present invention relates to a liquid crystal display system that includes a collimating backlight and a non-Lambertian diffuser. The present invention thus relates to liquid crystal display systems of the type that can be termed collimated backlit non-Lambertian diffused.
2. Discussion of the Related Art
Within this application, several publications are referenced by arabic numerals within parentheses. Full citations for these, and other, publications may be found at the end of the specification immediately preceding the claims. The disclosures of all these publications in their entireties are hereby expressly incorporated by reference into the present application for the purposes of indicating the background of the present invention and illustrating the state of the art.
Historically, it has been known in the prior art to illuminate liquid crystal displays. Liquid crystal displays of the type hereunder consideration are well-known to those skilled in the art. A conventional liquid crystal display is typically illuminated with a backlight device. Such a backlight device typically includes an illumination source located at one edge of a planar waveguide. For example, prior art liquid crystal display backlights have been based on a rectilinear waveguide having a transparent top surface and a metallized bottom surface. Such backlights are conventionally powered by a single fluorescent lamp located at one edge of the rectilinear waveguide, or by two lamps located at two edges.
As is known to those skilled in the art, the light from such an illumination source must be coupled into the waveguide in order to illuminate the liquid crystal display. In the past, this coupling has been inefficient. Thus, a previously recognized problem has been that much of the light available from the illumination source is wasted resulting in decreased brightness. Needless to say, it is desirable to provide a backlit liquid crystal display having higher brightness.
What is needed therefore is an apparatus that efficiently couples light from the illumination source into the waveguide. However, efficient coupling between the illumination source and the waveguide is not sufficient. Liquid crystal displays require collimated incident light and include a polarizer. Therefore, what is also needed is an apparatus that collimates and redirects the light from the illumination source so that the maximum amount of light from the illumination source can be coupled through the polarizer of the liquid crystal display. Collimation involves minimizing divergence. What is also needed is an apparatus that not only increases the brightness, but also provides anamorphic, (i.e., non-Lambertian), illumination, (e.g., different divergences in the horizontal and vertical directions).
Another previously recognized problem has been that liquid crystal displays are not bright enough for use in high ambient light conditions. Therefore, what is also needed is an apparatus that increases the brightness of a liquid crystal display. By increasing the overall coupling efficiency, a liquid crystal display will appear brighter. Alternatively, a lower power illumination source can be used to achieve the same brightness. Needless to say, it is desirable to provide a backlit liquid crystal display having lower power consumption.
Another previously recognized problem has been that the light transmitted through liquid crystal display systems is not homogeneous. Typically, the area of the liquid crystal display that is closest to the illumination source, or illumination spots, will be brighter. Therefore, what is also needed is a backlit liquid crystal display with more homogenous light distribution.
One unsatisfactory previously recognized approach, which attempts to solve the efficiency and homogeneity problems referred to herein, involves replacing the metallized bottom surface with a surface that includes a number of white dots. The density of the dots is proportional to the distance to the illumination source so that the backlight illuminates a liquid crystal display with greater homogeneity. However, this previously recognized approach has the disadvantage of relatively low coupling efficiency. Further, this previously recognized approach also has the disadvantage that the white dots do not collimate the light.
Moreover, this previously recognized approach also has the disadvantage of relatively high cost. The manufacture and sale of LCD systems is a competitive business. A preferred solution will be seen by the end-user as being cost effective. Therefore, what is also needed is a liquid crystal display system that is cost effective. A solution is cost effective when it is seen by the end-user as compelling when compared with other potential uses that the end-user could make of limited resources.
Yet another previously recognized problem has been that much of the light transmitted through liquid crystal display systems is wasted because it is not seen. The eyes of a viewer occupy a relatively localized position with respect to the liquid crystal display. The liquid crystal display will appear brighter if the light that is available from the liquid crystal display is directed to the viewer's eye. Therefore, what is also need is a backlit liquid crystal display having directionality. Heretofore, the above-discussed requirements have not been fully met.
The below-referenced U.S. patents disclose embodiments that were at least in-part satisfactory for the purposes for which they were intended. The disclosures of all the below-referenced prior U.S. patents, in their entireties, are hereby expressly incorporated by reference into the present application for purposes including, but not limited to, indicating the background of the present invention and illustrating the state of the art.
U.S. Pat. No. 5,390,276 discloses a backlight assembly utilizing microprisms. U.S. Pat. No. 5,365,354 discloses a GRIN type diffuser based on volume holographic material. U.S. Pat. No. 5,359,691 discloses a backlighting system with a multi-reflection light injection system. U.S. Pat. No. 5,253,151 discloses luminaire for use in backlighting a liquid crystal display matrix. U.S. Pat. No. 5,050,946 discloses a faceted light pipe. U.S. Pat. No. 5,202,950 discloses a backlighting system with faceted light pipes. U.S. Pat. No. 5,534,386 discloses a light source destructuring and shaping device.